The crayfish, Procambarus clarkii, medial giant axon is an unusual nerve model system because there is a large electrogenic transport contribution to its membrane potential coupled with its large size permitting axial electrode membrane space clamp (for current and voltage clamp) techniques for quantitative measurement of membrane electrical properties. This unique combination of properties presents the opportunity to study Na:K transport coupling ratio, transport system turnover rate, energy requirements of transport and transport efficiency from an essentially electrophysiological approach. Energy requirements of transport will be estimated by analysis of intracellular ATP, sodium, potassium and chloride concentration under the various alterations of extracellular ionic conditions and metabolic poisoning. Quantitative information concerning these transport properties will be derived from experiments where both intracellular and extracellular (Na) and (K) will be altered and specific metabolic poisons will be used to compare conditions of an operating pumping system to the same environmental situation with an inhibited transport system. Elucidation of these mechanisms and mode of operation of the transport system can provide direct insight into the interrelations among cation transport, modulation of nerve cell excitability, membrane steady-state ionic conductance control, voltage sensitive gated Na and K currents and conductance control.